The present invention relates generally to power transmission chains and particularly to an improved rocker joint for such chains. The rocker joint has a crescent shaped aperture and pair of pins. The invention has particular application to power transmission chains of the inverted tooth or silent chain variety, which are used in engine timing applications as well as in the transfer of power from a torque converter to a transmission or in a transfer case of a four-wheel drive vehicle or in vehicle transmissions. The invention also has application to chains of the roller chain variety as well as power transmission chains for use with variable pulley transmissions (continuously variable transmissions).
One type of power transmission chain is referred to as a silent chain. A silent chain is formed of interleaved sets of inverted tooth links which are constructed and arranged to contact the teeth of a sprocket. A set or rank of links is assembled from several links positioned alongside of or adjacent to each other. The links are connected by pivot means, which are typically round pins or rocker joint pins, received in a pair of apertures. Examples of silent chains are shown in U.S. Pat. No. 4,758,210 and U.S. Pat. No. 4,904,231, both of which are incorporated herein by reference.
A second type of power transmission chain is used to transfer power between a pair of variable pulleys in a continuously variable transmission. The chain links are provided in sets that are interleaved together. The links have aligned apertures for receiving pivot means. Load blocks or load carrying means that are positioned on the chain provide the means for transfer of power between the pulleys. An example of a chain suitable for use in a continuously variable transmission is shown in U.S. Pat. No. 4,911,682, which is incorporated herein by reference.
Another type of power transmission chain is known as a roller chain. A typical roller chain consists of alternate inner links and outer links. The inner links, which are also known as "bushing" links, consist of spaced sidebars with bushings tightly received in openings, or apertures, at each end of the sidebars. The outer links, which are also known as "pin" links or guide links, consist of spaced sidebars with pins tightly received in apertures at each end of the sidebars. The bushings freely rotate about the pins to pivotally connect the outer links to the inner links in alternate arrangement. Rollers are mounted for rotation about the bushings. An example of such a roller chain is shown in U.S. Pat. No. 4,186,617, which is incorporated herein by reference.
Silent chains in which a plurality of link plates are joined by rocker joints consisting of a pair of rocker pins have been widely used in prior art. An example of such silent chain is disclosed in the Examined Japan Patent Application 41-2805. In the silent chain disclosed in Application 41-2805, the link plates are provided with apertures at both ends. The apertures have a crescent shape with a convex circular arc support surface. The rocker pins are inserted in the apertures and have a circular arc section with a convex rocker surface and a concave seat surface. The pins are engaged at their seat surface with the aperture support surface. However, since the rocker pin has a circular arc section, the pin section area is relatively small and the chain often ruptures due to the fracture of the pins.
A silent chain in which such fracture of pins is prevented is disclosed in Examined Japan Patent Application 1-55821. In this silent chain, the rocker pins are reinforced by installing a reinforcing plate at the inner surface of the guide link plate. The drawback of this silent chain is that the total width of the chain is increased by the width of the reinforcing plate. The simplest way to prevent such fracture of the pins is to increase the section of rocker pins (to increase the radius of curvature of the rocker surface). In this case, however, the hole becomes large in comparison with the link contour of the link plates, and, consequently, the strength of the link plates decreases.
Another example of the silent chain of the conventional rocker joint type is disclosed in Examined Japan Patent Application 51-1815. In this silent chain, the rocker pins have a nearly trapezoidal cross section of large area. As a result, the strength of pins in such a silent chain is much higher than that in the above-described conventional rocker pins. However, the drawback of this silent chain is that a pair of inclined surfaces, which form a surface stopping the rolling of the rocker pin when load is applied to the chain, make an acute angle. Therefore the tolerance between the inclined surface of rocker pin and the respective inclined surface formed by the aperture in the link plate easily expands in the pitch direction of the chain. For this reason, the manufacture of the chain having a certain pitch becomes a very difficult task.
Another example of the conventional silent chain of the rocker joint type is disclosed in Unexamined Utility Model Application 62-196950. In the silent chain according to this application, the rocker pins have approximately elliptical section, which provides for a higher strength of the rocker pins than in the first of the above-described conventional examples. However, in such silent chain, a protrusion is formed in the aperture of the link plate. The protrusion is used to stop the rotation of rocker pins when the chain is bent. When an impact load is applied to the chain, the protrusion tends to slip, and creates a relative slip between the rocker pin and the link plate and increases the wear of these parts. Moreover, such protrusions cause manufacturing problems because they require difficult machining, accompanied by significant wear of tools.
Another example of a silent chain of the conventional rocker joint-type is disclosed in U.S. Pat. No. 5,372,554, which is incorporated herein by reference. Each of the rocker pins is bounded by a circular arc rocker surface, a circular arc seat surface opposite to this rocker surface and concentric with this rocker surface and a pair of side surfaces connecting the rocker surface and the seat surface. Each pin side surface consists of a circular arc having its center of curvature located within the body of the pin. The pin side surface also includes a substantially plane surface of a slight arc connected to the circular arc. The aperture is bounded by a circular arc support surface located at the end portion of the link plate that engages with the seat surface of one of the rocker pins. The aperture includes a retention surface connected to the support surface and facing the side surface of the rocker pin. The aperture also includes a curved surface connected to the retention surface with sufficient clearance to allow rotation of an adjacent rocker pin. Because of the shape of the rocker pins and apertures the aspect ratio (i.e. ratio of height to width) is lower than the aspect ratio associated with conventional circular rocker pins and apertures. The reduction in aspect ratio leads to an increase in the strength of the chain. However, because the pin side surface has its center of curvature located in the section of the rocker pin at which the seat surface contacts the support surface, the reduction in the aspect ratio is limited.
It is thus desirable to provide apertures and rocker pins with even lower aspect ratios to further increase the strength of the chain.
The present invention relates to a rocker joint for chain. More specifically, in its preferred embodiment, the present invention relates to a silent chain in which tensile strength and wear resistance are increased due to the improvement of the shape of the section of the rocker joint and the shape of the pinhole or aperture in the link plate accommodating this rocker joint.